This disclosure relates generally to an apparatus and a method for supplying anesthetic agent to an anesthesia system. The disclosure also relates to an anesthesia system for providing an inspiration gas to lungs of a subject.
On general anesthesia anesthetic drugs are used to induce and maintain patients experiencing surgical operation relaxed motionless, unconscious, and free from pain. The anesthetic drugs interfere on the central nervous system for these effects. On inhalation anesthesia anesthetic drugs are delivered through patient breathing to lungs where they get diffused to patient blood circulation. This circulation further carries the drug to the effect site in brains.
Inhalation anesthesia drugs are halogenated hydrocarbons that are delivered on administration site as liquids. These liquids are very volatile with vapor pressure at room temperature varying between 20-90 kPa. These liquids are vaporized for patient breathing in anesthesia vaporizer. The most common inhalation anesthesia drugs are isoflurane, sevoflurane and desflurane. These have replaced the use of their predecessors, halothane and enflurane.
For various reasons preference of the agent to be used may vary between patients and clinics. The vaporizers are heavy devices to enclose thermal energy for the cooling caused by liquid vaporization. The devices are positioned high over table top for convenient use of the output concentration dial. Therefore their installation on the anesthesia system may be laborious for clinical personnel. For this reason the anesthesia machines are equipped with functionality that enables easy selection of the agent to be used. Anesthesia system accommodates therefore often two or three sockets to connect the vaporizer. As separate, anesthesia system independent, module provides also advantage to have functional redundancy against vaporizer failure.
In operation, vaporizer receives fresh gas, which is a mixture of oxygen, nitrogen, and nitrous oxide, and completes that with required percentage of the anesthetic drug vapor. On state-of-the-art vaporizers the completion occurs with passive vaporization of the liquid agent respective to its vapor pressure. This prepared gas is then delivered from vaporizer outlet to anesthesia breathing system for further delivery to patient.
Arising from the principle of vaporization to the vapor pressure, if two vaporizers would be connected in series they both deliver the required concentration to the passing gas stream. Both of these drugs would then get delivered for patient breathing and circulation to effect-site both drug causing their effect resulting to doubled strength of the anesthesia effect. Clinically such situation is challenging to manage and therefore vaporizer constructional requirement standards require mechanisms that prevents simultaneous opening of the vaporizers.
State-of-the-art anesthesia systems include sockets to mount the vaporizers side-by side. The vaporizers designed for these sockets have mechanical pins protruding out from the vaporizer enclosure from its side adjacent to the other vaporizer when the vaporizer is activated from their concentration control dial. This protruding pin then prevents the other vaporizers connected to the system get activated when their pin have no more room for protrusion in colliding with the pin of the already activated vaporizer. These anesthesia systems are designed for mechanical vaporizers.
Modern anesthesia systems are electronic except the vaporizers where the traditional mechanical actuation including interlocking and passive vaporization still dominates. These devices lack in performance what electronics can bring along regarding e.g. therapy data recording to patient records, diagnostics, measuring drug usage, monitoring drug level and external control of the desired output from anesthesia system.
Electronics as part of anesthesia vaporizer would thus bring many benefits to the anesthesia system. Provision of the mechanical interlock with moving parts and arms is however impractical electronically in requiring mechanical movement. Such systems would require actuators generating this movement as well as sensors sensing whether the movement of adjacent vaporizer has occurred preventing the opening of another vaporizer.
External electronic control of the vaporizer from anesthesia system allows positioning of the vaporizers beyond the prime user interface area as well as anesthesia automation. Provision of electrical energy for vaporization miniaturizes size and weight. These enable anesthesia system miniaturization, and even positioning of the vaporizer to prime user interface for manually control of the vaporizer from the embedded controls.